Animation nodes: bake Cycles Material Output to keyframes - possible?
After further search I think there is no node for this.
Now I did it with a quick an dirty script-node:
    # inputs:
# Enable = boolean
# SetKeyframes = boolean
# RemoveUnwanted = boolean
# MaterialName = text
# pframe = integer

import bpy

mat = None

if Enable:
    for tmat in bpy.data.materials:
        if tmat.name == MaterialName:
            mat = tmat
    if mat != None:
        print ('material found')
        emitStr = mat.node_tree.nodes['Emission'].inputs[1]
        if RemoveUnwanted:
            try:
                emitStr.keyframe_delete( 'default_value', frame=pframe)
            except:
                None
        if SetKeyframes:
            emitStr.keyframe_insert( 'default_value', frame=pframe)
            
    else:
        print ('material '+MaterialName+' not found')
        return